Biological Knee Replacements

"The 'biological knee replacement'

- the alternative to an 'artificial' knee replacement"

Modern knee replacements are very good - patient reported outcome scores show 90+% good-to-excellent results, about 95% of prostheses are still working at 10 years follow-up and about 80 to 85% at 20 years follow-up. Furthermore, the field of knee replacement surgery continues to move forward, with regular advances in techniques, prostheses and materials.

However, one of the major problems facing Orthopaedic Knee Surgeons today is the increasing number of people needing knee replacements and the changing demographics of the patients we see - in that younger and younger patients seem to be presenting with severely worn / degenerate / arthritic knees needing treatment. The reason for this is most probably multifactorial -

  • Due to the awareness of the general benefits of cardiovascular fitness, more an more people are participating in vigorous exercise and sports, through to older and older ages. Whilst exercise is good for you, it could be argued that sport is bad for you (from an injury perspective).
  • People's attitudes to growing old have changed, and increasing people nowadays expect to be able to continue with vigorous activities, exercise and sport well into their 50s and beyond.
  • People's expectations about what surgery can do for them have increased significant, in parallel to the fantastic technological advances in knee surgery that we have seen over the last 30 years, in particular. As the results of knee replacement surgery continue to improve, people's threshold for actually having knee replacement surgery correspondingly drops.

Although knee replacements generally are exceptionally good at relieving pain and improving movement and function in patients with severely arthritic knees, there is a significant issue with putting in knee replacements in younger patients -

  • the younger the patient, the greater the forces and impact an artificial knee replacement will be subjected to
  • younger patients are also more mobile, and therefore the knee prosthesis will also be subjected to more movement cycles
  • these factors increase the wear rates on a knee prosthesis, meaning that it will 'wear out' and fail sooner in a younger person that in an older, less active individual
  • although artifical knee replacements will tend to fail quicker and earlier in younger patients, the younger patients will tend to live longer, and therefore actually need their knee prosthesis to last longer
  • if a knee replacement prosthesis fails, then it can be replaced with a new one - a revision knee replacement. However, the revision operation is longer, technically more demanding (there is less bone present to fix the prosthesis to), has a higher risk of complications and the revision prostheses tend to give poorer patient reported outcomes and last less long that the original primary knee replacements.

For all there reasons, surgeons always try to delay putting in knee replacements in younger patients unless it is an absolute necessity and a last resort.

Correspondingly, surgeons continue to look for good effective alternative options to artificial knee replacement surgery. One such option is the concept of the 'biological knee replacement' - a term made popular by Dr Kevin Stone, of The Stone Clinic in San Francisco.

The biological knee replacement

The two types of cartilage in the knee are -

- articular cartilage - this is the smooth, white, shiny, thin layer of glistening tissue that covers the surfaces of the ends of the bones, making them very low friction

- the meniscal cartilages - these are two crescent shaped elastic cartilages sitting inside the knee joint, in between the bones, acting as shock absorbers and load sharers.

In wear & tear / degeneration / arthritis of the knee, both of these types of cartilage end up suffering wear and they can tear or be eroded away. If the meniscal cartilages are torn or removed then the forces on the articular cartilage will be significantly elevated, increasing the speed of onset and severity of arthritis. With arthritis, the articular cartilage wears away, eventually leaving areas of exposed bare bone in the knee.

Surgical techniques already exist for trying to repair (instead of trim or remove) torn meniscal cartilages. Techniques also exist for trying to replace missing meniscal cartilages, through the use of either meniscal scaffolds or replacing the entire meniscus with a donor graft - meniscal allograft transplantation.  Also, there are already various techniques available for trying the repair/replace damaged or missing patches of articular cartilage, such as microfracture, MACI (Matrix-induced Autologous Chondrocyte Implantation/transplantation) or, more recently, the use of artificial scaffolds such as the Chondrotissue graft.

  Chondrotissue Graft being prepared 
   Articular cartilage (chondral) defect on the end of the femur
  Chondrotissue Graft (red) fixed in place and filling defect.

However, up until very recently, most surgeons agreed that there was little point in replacing missing articular cartilage if the meniscal cartilage in that side of the knee was also missing - as the new cartilage graft would be subjected to undue increased pressures, with a significant risk of failure. Similarly, until recently, most surgeons would have considered Grade IV cartilage damage (exposed bare bone) a contraindication to performing Meniscal Allograft Transplantation - because the hard, rough surfaces of the bare bone would abrade the meniscal graft, again leading to premature failure.

Thankfully, however, an alternative approach to the treatment of severely damaged knees in younger patients is now available - the 'biological knee replacement'. The concept here is quite simply to replace both the missing articular cartilage and the damaged meniscal cartilage tissue in the knee at the same time, on the premise that doing only one without the other increases the risks of failure, and doing both at the same time protects each 'half' of the reconstruction.

This may not seem like 'rocket science' and may appear rather obvious. However, it is only in fairly recent years that the surgical techniques for each of meniscal transplantation and articular cartilage replacement have improved - both in terms of technical feasibility/ ease and proven outcomes / results - and that some surgeons (that small number of highly specialized knee surgeons actively involved in this field) are now familiar enough and comfortable enough with the surgical techniques to be able to offer both simultaneously.

   Medial compartment of a knee with a missing medial meniscus.
  Same knee after replacment of the medial meniscus by meniscal allograft transplantation.

Thus, unlike an 'artificial' knee replacement, where the ends of the bones are covered in metal and there is a polyethylene spacer in between, the 'biological knee replacement' replaces a layer of living articular cartilage over the surfaces of the bones, with a living elastic meniscal shock absorber in between the two surfaces.

The Results

There is just a small number of knee surgeons in the UK actively involved and experienced in the development of meniscal replacement surgery. Mr Angus Strover (London Sports Orthopaedics) was the UK's first knee surgeon to perform a meniscal transplant, and has now performed probably more meniscal transplants than any other UK surgeon. Mr Ian McDermott (also of London Sports Orthopaedics) has performed extensive lab-based and clinical research into the field of meniscal repair, replacement and transplantation, and has worked closely with Mr Strover for a number of years and also offers this surgery, and is now one of the UK's leading authorities on the subject - having published extensively in the medical/scientific literature and presented and lectured at numerous scientific meetings. The surgeons in London Sports Orthopaedics are currently conducting a study, looking at the outcomes/results of their patients with combined meniscal & articular cartilage replacement.

Recently, Dr Kevin Stone from San Francisco, published the results of his series of patients. In his study, there were over 100 patients, half of which were aged over 50, with a maximum follow-up of 12 years and an average follow-up of 5 years. Of these patients, only 15% progressed to full (artificial) knee replacement surgery, and these were at an average of 5 years after 'biological knee replacement' surgery. The estimated mean survival time (for continued success of the knee surgery) was 10 years.

The Surgery and the Rehab

The actual surgery, whilst not majorly invasive, is technically demanding and fairly complex. Most of the procedure can normally be done via keyhole surgery (arthroscopy), but normally some moderately small incisions do need to be made for inserting the actual grafts into the knee.

The surgery itself can take anything from 2 to 3 hours and is performed normally under a general anaesthetic, with a 1-night post-op stay in hospital.

It is vital, however, that after this kind of surgery patients adhere strictly to a very specific rehab regime, to protect the grafts and allow them to heal properly. This rehab involves staying on crutches for the 1st 6 weeks, with a hinged knee brace, followed by 6 weeks of very gentle careful physiotherapy (normally keeping 1 crutch). This takes one up to the 12 week (3 month) mark, at which point most patients are then ready to start more vigorous physiotherapy rehabilitation exercises. However, patients must not do any kind of impact exercise (including running) until a full 9 months post-op, in order to protect the grafts as they are healing. Failure to stick to this regime can cause the graft(s) to tear or fail.

Importantly, prior to actually proceeding with this kind of major reconstructive surgery, it is vital that your surgeon checks exactly what is going on inside your knee, to tidy up the joint and to ensure that your knee is actually suitable for the reconstructive surgery. Therefore, it is nearly always necessary to evaluate the knee first with a knee arthroscopy (simple keyhole surgery) prior to subsequently proceeding with any more major reconstructive procedures. Meniscal allografts are highly valuable human tissue grafts that are only ever issued on a named-patient basis, and therefore cannot be kept 'in reserve' or 'just in case' - instead, surgery of this nature has to be confirmed carefully in advance first, and then planned and specifically booked.


How can I find out more?

If you have knee problems and you think that your knee might potentially be suitable for this kind of surgery, then you will need to be seen in clinic by one of our specialist surgeons for a full and detailed assessment. This will normally require a 1-hour clinic appointment, and patients will normally also need a full set of X-rays and an MRI scan of the knee.

CONTACT US

Article written by
Mr Ian McDermott
Knee Surgeon
London Sports Orthopaedics
Northwood Sports Orthopaedics

Last updated 20/09/2010